Figure 7. Effects of toxin CvIV4 on activation and inactivation of isoform Na_v1.7 expressed in Hek293 cells.

A. Depolarizing pulses in 5-mV increments were used to elicit current from Na_v1.7 expressed in HEK cells before (B) and after (C) the application of 1 µM CvIV4. D. Effects of 1 µM toxin on the current-voltage relationship of Na_v1.7. Currents not inactivated at 5 ms in the presence of 1 µM toxin were plotted as the percentage increase in the fraction of current at 5 ms (I_{5 ms}). E. Effects of CvIV4 on steady-state activation and inactivation of Na_v1.7. When data points were fitted with a Boltzmann equation, the V1/2 values were −90.2±1.2 and −94.1±1.6 mV before (filled circles) and after (open circles) toxin treatment, respectively. F. Effect of CvIV4 on rate of recovery from inactivation at −100 mV. Cells held at −100 mV were given a depolarizing prepulse to 0 mV for 20-ms followed by a step back to −100 mV with increasing duration to allow channels to recover from inactivation, followed by a 20-ms test depolarization of 0 mV to activate those channels that had recovered from inactivation. Data points presented as a fraction of the maximum recovered current were fitted with single exponential function to estimate the time constant. The time constants were 58.7±15.4 and 48.2±15.3 ms before (filled circles) and after (open circles) toxin treatment, respectively.